Another month, and my alternative theories on planetary formation are still alive. Most of the information that I could find was not directly relevant, but nevertheless there were some interesting papers.
 
One piece of interesting information (Science 341: 260-263) is that analysis of the isotopes of H, C and O in the Martian atmosphere by Curiosity rover, and comparison with carbonates in meteorites such as ALH 84001 indicate that the considerable enhancement of heavy isotopes largely occurred prior to 4 Gy BP, and while some atmospheric loss will have occurred, the atmosphere has been more or less stable since then. This is important because there is strong evidence that there were many river flows, etc on the Martian surface following this period, and such flows require a significantly denser atmosphere simply to maintain pressure, and a very much denser atmosphere if the fluid is water, and the temperature has to be greater than 273 ^oK. If the atmosphere were gradually ablated to space, there would be heavy isotope enhancement, so it appears that did not happen following 4 Gy BP. If there were such an atmosphere, it had to go somewhere other than space. As I have argued, underground is the most likely, but only if nitrogen was not in the form N₂. It would also not be lost due to a massive collision blasting the atmosphere away, the reason being there are no craters big enough that were formed following the fluvial activity.
 
There was one interesting piece of modeling to obtain the higher temperatures required for water to flow. (Icarus 226: 229 – 250.) The Martian hydrological cycle was modeled, and provided there is > 250 mbar of CO₂ in the atmosphere, the model gives two "stable" states: cold and dry, or warm and wet, the heat being maintained by an extreme greenhouse effect arising from cirrus ice crystals of size > 10μm, even with the early "cool sun". One problem is where the CO₂ came from, because while it is generally considered that Earth's volcanoes give off CO₂, most of that CO₂ comes through subduction, and Mars did not have plate tectonics. Whether this model is right remains to be seen.
 
There was one paper that annoyed me (Nature 499: 328 – 331). The problem is that if Earth formed from collisions of protoplanetary embryos, the energy would have emulsified all silicates and the highly siderophile elements (those that dissolve in liquid iron) should have been removed to the core nearly quantitatively. Problem: the bulk silicates have these elements. An analysis of mantle type rock have chalcogen ratios similar to Ivuna-type carbonaceous chondrites, but are significantly different to ordinary and enstatite chondrites. The authors argue that the chalcogens arrived in a "late veneer", and this contributed between 20 -100% of the water on earth. What has happened is that the authors carried out a series of analyses of rocks and to make their results seem credible, Earth had to be selectively but massively bombarded with one sort of chondrite, but none of the more common ones. Why? The only reason they need this rather strange selection is because they assumed the model in which Earth formed through the collision of planetary embryos. If the Earth accreted by collecting much smaller objects, as I suggest, the problem of the chalcogens simply disappears. It is interesting that the formation of planets through the collision of embryos persists, despite the fact that there is reasonable evidence that the rocky planets formed in about 5 My or less, the Moon formed after about 30 My due to a collision with something approaching embryo size, and modeling shows that formation through such embryo collisions takes about 100 My. The time required is far too long and the evidence is that when there is such a collision, the net result is loss of mass, except possibly from the core.
 
A paper in Angew. Chem Int Ed. (DOI: 10.1002/anie.201303246) showed a convincing mechanism by which hydrogen cyanide can be converted to adenine. This is of particular interest to me because my suggested mechanism for the formation of ATP and nucleic acids is also photochemically assisted. If correct, life would have commenced in vesicles or micelles floating on water.
 
On a positive note (Nature 499: 55- 58) the authors noted that while most stars form in clusters, some are also in loose clusters with stars density at less than 100 per cubic parsec. One problem might have been that stars born in loose clusters might be the only ones that can retain planets, however the authors report transits in two sun-like stars in a dense cluster, which shows that planets can survive in such a cluster, and that the frequency of planet formation is independent of the cluster density. This makes extrasolar planets very much more probable.